Solar system size calculator
Find out how big a solar system your home needs to cover your electricity use. Enter your usage and your location's sun hours to get a system size in kilowatts and an approximate panel count.
How it works
- Takes your annual or monthly electricity usage.
- Divides by your location's average peak sun hours and typical losses.
- Returns a system size in kW and an estimated number of panels.
What changes your result
- Your annual electricity use in kWh
- Local peak sun hours, which vary widely by region and season
- System losses of roughly 15–20% from heat, wiring and the inverter
- Panel wattage and how much unshaded roof area you have
Frequently asked questions
What size solar system do I need?
It depends on your electricity use and local sun. As a rough guide, every 1,000 kWh used per year needs about 0.7–1 kW of solar. This calculator sizes it precisely from your usage and local sun hours.
How many solar panels does a house need?
Most homes need 15–25 panels. The count depends on your usage, panel wattage (commonly 400–450 W today) and roof space. Fewer high-wattage panels can reach the same size in less area.
Should I size solar to cover 100% of usage?
Not always. Net-metering rules, roof space and budget all matter. Some owners offset 80–90% to avoid over-producing under poor export rates. Check your utility’s terms before finalising size.